The present invention relates to a portable boring and welding machine.
In particular, the present invention relates to a portable boring and welding machine of the type normally used to recondition bores or seats for crankpins, cylinder liners, etc., directly on a machine or part of a machine without having to transport the part to be repaired to a workshop and without having to place the part on a fixed machine tool.
This need is felt especially strongly when repairing the rotating parts of large construction machines such as excavators and cranes or parts of fixed installations that are difficult to dismantle and transport.
A typical example of the use of a portable boring and welding machine is boring (or reaming) a bore to be reconditioned, then adding material by welding and finally finishing the bore by boring (or reaming) to restore the original dimensions and tolerances.
For this purpose, machines with three drive motors are known. The three drive motors are designed to rotate the welding tool used to add material to the inside of the bore, to rotate the boring tool and to drive the tool backwards and forwards along the axis of the bore being machined.
These triple-motor machines are extremely complex on account of the large number of components and, in an attempt to provide a simplified solution, machines with only two motors have been constructed.
Twin-motor machines, although they are much more simple, are not entirely satisfactory: transmission of rotational motion is accomplished by flexible transmission means, such as elastic belts, whose tension must be kept at a defined optimum level using special tensioning devices.
The drive belt must transmit rotational motion to the tool shaft not only during boring/reaming operations but also during the step of adding material by welding. Obviously, the power required for these operations differs considerably and may also vary significantly on account of the differences in diameter of the bores machined, leading to high resistant torque moments and the need for the drive belt to operate within a very wide tension range.
The above mentioned tensioning devices are therefore unable to guarantee the correct belt tension for all the different working conditions, which leads to poor machine performance.
Another drawback closely connected with the use of flexible means for transmitting rotational motion is due to the vibrations created during machining which are propagated from one machine part to another and which have a negative effect on the flexible transmission means.